To improve the diagnosis of renal diseases by in vivo imaging techniques, new radioactive agents will be synthesized to achieve a high renal extraction efficiency and a low hepatic extraction, which can be labeled with Tc-99m. These compounds will contain bifunctional chelates such as iminodiacetic acid, ethylenediaminediacetic and nitrilotriacetic acid or sulphur-containing ligands. Labeled low molecular weight proteins will also be explored as renal radiopharmaceuticals. Abnormal renal accumulation of Tc-99m diphosphonates will be evaluated as a means of detecting abnormalities of renal calcium metabolism in drug-induced or ischemic renal tubular degeneration, and in stone-forming animals. To quantify counting rate data of renal radioisotope studies using scintillation camera-computer techniques, mean renal contrast transit times will be measured after deconvolution analysis. The results will be compared with measurements of renal blood flow and histological changes in dogs with three different types of unilateral renal ischemia. Serial transmission CT imaging of the kidneys following contrast medium injection will be compared with the nuclear methods for the detection of unilateral ischemia.